1. Field of the Invention
The present invention generally relates to fuel-discharge systems and, more particularly, to a fuel-discharge protection system for preventing electrostatic hazard.
2. The Prior Arts
Grounding is often considered an extremely important issue in preventing electrostatic hazard. However, despite the technology advances, a reliable and effective grounding still seems a difficult job. Accidents due to improper grounding are still quite often, even for high-tech manufacturers.
For gas stations, electrostatics, if not treated seriously and cautiously, could cause severe property loss and human lives too. In order to avoid such accidents, relevant industries and agencies have enacted very strict regulations. For example, a petroleum company may require specifically that its franchised gas stations to have a ground resistance below 50Ω from their fuel outlets. Nevertheless, despite the strict rules and regulations, most gas stations still adopt a traditional fuel-discharge system with an un-reliable grounding as described below.
FIG. 1 is a schematic view showing how a tank truck conventionally discharges fuel into a fuel reservoir. As shown in FIG. 1, a tank truck 10 is parked besides a fuel inlet 22 of an underground fuel reservoir 20. An operator first connects the body of the tank truck 10 to a ground bar 30 buried in the ground via a conduction cable 40 to hence eliminate the static electricity carried on the truck's body. Then, the operator connects a fuel outlet 12 of the tank truck 10 to the fuel inlet 22 of the fuel reservoir 20 through a fuel pipe 50, so that fuel can flow into the fuel reservoir 20 when the operator opens the fuel outlet 12 of the tank truck 10. After fuel is discharged, the operator should close first the fuel outlet 12, dismount the fuel pipe 50, and finally disconnect the ground conduction cable 40.
In the foregoing conventional fuel-discharge system, a ground bar 30 buried underground provides inadequate grounding as the ground bar 30 would degrade gradually over time. The rust developed on the ground bar 30 would result in a greater contact resistance and even cause the ground bar 30 to be unusable. Under such a poor grounding, mounting or dismounting the fuel pipe 50 may induce sparks from static electricity to kindle the tank truck 10 or the oily gas of the fuel reservoir 20, causing a severe explosion. In real life, static electricity is not a constant substance as its name may imply, on the contrary, it could be accumulated over time to generate an instantaneous current as high as 1.5 amperes according to academic reports. Besides, the grounding quality would vary with different weather conditions. For example, the contact resistance of the ground bar 30 may meet requirements in a damp or raining day while it may not in a dry and cool day.
Therefore, for avoiding electrostatic-related accidents in gas stations, there are demands for improving the existing fuel-discharge system.